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Nursery & Forest

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Nursery & Forest
Volume 63 Number 15 Date 08/16/2018

BROWN ROT - This destructive fungal disease was recently observed on American plum trees in Oneida County. Brown rot infects trees and shrubs in the cherry and plum genus Prunus, seriously impacting fruit production and causing losses of 50% or more prior to harvest. Infected fruits exhibit powdery grayish-brown specks that expand to envelop the entire fruit. The fruit later dries and shrivels up to form "mummies." Characteristic powdery, gray masses of spores form on the surfaces of both rotting fruits and mummies.

To reduce future infections, all rotted fruit should be removed and destroyed. In addition, infected twigs should be pruned four to six inches below sunken or dead tissue on each branch. Decontaminate tools between each cut by dipping them for at least 30 seconds in a 10% bleach solution or preferably 70% alcohol. Brown rot is not a lethal disease, but once fruits are infected, there are no curative treatments.

FOLIAR NEMATODE - Hosta plants at a northwestern Wisconsin nursery grower were showing symptoms indicative of infestation by foliar nematodes. These microscopic worm-like organisms live on and within the leaf tissue of hundreds of herbaceous and woody ornamental plant species. Nematode infestation can cause stunting or twisting of foliage in young plants, and often produces angular, necrotic leaf streaks bordered by leaf veins in mature plants. The symptoms become more pronounced and recognizable later in the growing season. This pest is readily spread among plants by splashing water, such as from rainfall or overhead irrigation. Reducing leaf wetness is advised to prevent the nematodes from spreading. Replanting susceptible stock in areas recently infested with nematodes should be avoided since the nematodes can temporarily survive in soil. Cuttings from infected stock should never be used for propagation, and decontamination of tools following contact with plants suspected of being infected is good practice. Chemical control is not effective against this pest.

TAR SPOT - This late-season leaf blight disease is developing on maple trees across Wisconsin. The pale yellow lesions now apparent will soon become raised, black, tar-like lesions. Tar spot is an aesthetic disorder best con-trolled by clearing and disposing of infected leaves in fall to prevent the spores from spreading. In rare cases where treatment is warranted, three fungicide applications are necessary for control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded.

OAK TWIG PRUNER - Boring by the larval stages of this oak pest in small branches and twigs can result in considerable branch-drop by late summer. If lawns are covered with twigs and branches 20-40 inches long with the leaves still attached, the oak twig pruner is likely the cause. Property owners should look for a small plug of wood or frass at the end of the twig to confirm. Hardwood trees attacked by this beetle may be seriously damaged but are usually not killed. The most effective control is to collect and burn the fallen branches in autumn or winter.

-- Timothy Allen, DATCP Nursery Inspector